JPS5810509B2 - Novel water-swellable fiber and method for producing the same - Google Patents

Description

Detailed Description of the Invention The present invention provides an outer layer of a hydrophilic crosslinked polymer (hereinafter referred to as hydrogel) and an inner layer of an acrylonitrile polymer (hereinafter referred to as AN polymer) and/or another polymer. The present invention relates to a novel water-swellable fiber that has a multilayer structure, has latent or actual crimp, and has high water-swellability and high physical properties, and a method for producing the same.

In recent years, highly water-swellable polymers have attracted attention for their special functions and are being applied to a wide range of fields of use.

For example, the ability of such polymers to instantly absorb large amounts of water can be used to make diapers, sanitary products, etc., the ability to retain moisture can be used to make soil conditioners, instant sandbags, etc., and the compatibility with human tissue can be used to develop polymers. soft contact lenses, artificial organs,
Attempts have been made to apply it to surgical suture materials, and some of these applications have already entered the stage of practical use.

It is often preferable for water-swellable polymers (hydrogel), which have a wide range of applicability, to be in the form of fibers depending on the intended use. .

However, although such existing natural or synthetic fibers have a certain degree of water swelling ability, their degree of water swelling is extremely low, or they are water soluble, and in any case, their own weight is very low. It was far from the standard of water-swellable fibers, which can absorb and retain anywhere from twice as much water to several hundred times as much, and are water-insoluble.

Further, Japanese Patent Publication No. 52-42916 describes a highly swellable fibrous structure obtained by introducing a specific crosslinked structure and a large amount of carboxyl groups in the form of salt into acrylic fibers.

However, in such fibrous structures, extremely large amounts of carboxyl groups in the form of salts are introduced, and the entire inner and outer layers of the fibers are hydrogel-formed, so they certainly have a high degree of water swelling performance. However, it was extremely brittle and had physical properties far from the concept of fiber.

That is, the reality is that water-swellable fibers with satisfactory performance still do not exist, and imparting high water-swellability and maintaining fiber physical properties are contradictory issues.

Here, as a result of intensive studies to overcome the above-mentioned essential difficulties and provide a high degree of water swelling property while maintaining the fiber physical properties, the present inventors have found that the present inventors have found that the fibers have latent or actual crimp and are AN-based fibers. By applying a specific alkali metal hydroxide aqueous solution to a fiber made of a polymer (hereinafter abbreviated as AN-based fiber), only the outer layer of the fiber is selectively hydrophilically crosslinked (hydrogelated). Discovered the fact that water swelling performance can be advantageously imparted without impairing crimp performance and fiber properties,
We have arrived at the present invention.

That is, an object of the present invention is to provide a novel water-swellable fiber that has latent or actual crimp and also has high water-swellability and high physical properties, and a method for producing the same.

The water-swellable fiber according to the present invention for achieving the above object is composed of an outer layer made of human staghorn gel and an inner layer made of AN polymer and/or other polymer, and It has obvious crimps and has a salt-type carboxyl group represented by -coOX (X: alkali metal or NH4).
．． Contains 5-5.0 mmo1/7 and 3-300 CC
/1 water swelling degree and high physical properties, and such water swelling fibers have a water swelling degree of 6.0 mol/1000? Highly concentrated alkali metal hydroxide aqueous solution, or 0.5 mol/10
By applying a low concentration alkali metal hydroxide aqueous solution coexisting with an electrolyte salt at a concentration higher than the 00P solution to hydrogel the outer layer of the fiber, the outer layer consisting of a hydrogel and an AN-based polymer and/or others are formed. and an inner layer made of a polymer, and has latent to actual crimp,
Moreover, the salt-type carboxyl group represented by -COOX (X: alkali metal or NH4) is contained in an amount of 05 to 5.0 mmol/?
Contains and 3 to 300 CC/? It can be advantageously produced by forming the fiber into a fiber having a degree of water swelling and high physical properties.

The AN-based polymer according to the present invention is a general term for polymers containing AN as a copolymerization component, and is an AN homopolymer or AN and one or more other ethylenically unsaturated compounds. or a graft copolymer of AN and other polymers such as starch, polyvinyl alcohol, etc.
AN-based polymers and other polymers, such as polyvinyl chloride-based,
Examples include mixed polymers with polyamides, polyolefins, polystyrenes, polyvinyl alcohol groups, celluloses, and the like.

The content of AN in such an AN-based polymer is 30
It is desirable that the AN content is at least 50% by weight, preferably at least 50%, and the AN content is less than this recommended range.
When using fibers consisting of the following as a starting material, it is not preferable because it is not sufficiently hydrophilized by alkaline hydrolysis treatment, or even if it can be made hydrophilic, it is difficult to form water-swellable fibers.

In addition, there are no particular restrictions on the polymer composition, such as the type of the ethylenically unsaturated compound that is the copolymerization component of the AN polymer or the molecular weight of the polymer, and the required performance of the final product,
It can be arbitrarily selected depending on the copolymerizability of the monomers, etc.

Furthermore, methods for producing these polymers and methods for forming fibers with latent or actual crimp from the polymers can be made from known methods (for example, single-component spinning, sheath-core composite spinning, etc.). Can be selected arbitrarily.

In other words, the AN-based fibers having latent or actual crimp that can be employed in the present invention include the AN-based fibers that are easily hydrolyzed under the conditions of the subsequent hydrolysis treatment, in addition to the fibers made of the single AN-based polymer component. A polymer is used as a sheath component, and a hydrolyzed AN-based polymer is used as a core component, or the AN-based polymer is used as a sheath component, and another polymer (for example, the above-mentioned polyamide-based, polyolefin-based, etc.) is used as a core component. Sheath-core type composite spun fibers such as core component fibers, fibers made by randomly spun composites of two or more component polymers, sea-island type composite fibers, two-component laminated type composite fibers, or sand inch type composite fibers Specific spun fibers such as composite fibers can be mentioned, and as long as such fibers have latent or actual crimp, they can be employed as the starting material of the present invention.

Note that self-crimping type fibers such as two-component bonding type, random composite spinning type, eccentric sheath-core type, sea-island type composite fibers, etc. It has excellent crimp-retaining ability, and for example, crimp does not disappear easily under alkali treatment conditions, or if desired, latent crimp can be brought to light during alkali treatment. It is preferable to use it as

In addition, the self-crimping type fiber may be used after making the crimps obvious by heat treatment, or without making the crimps obvious, or by making the crimps obvious and then using hot stretching or the like. It is also possible to use the fiber in a state where the crimp is made latent by eliminating the crimp, and furthermore, the fiber is made by imparting mechanical crimp to the self-crimping type fiber having the latent or actual crimp.
It goes without saying that it can be suitably employed as a starting material for the present invention.

The latent or actual crimp properties of such AN-based fibers are generally maintained under the alkali treatment conditions recommended in the present invention, and therefore water-swellable fibers that ultimately have the crimp properties of AN-based fibers are obtained. almost uniquely determines the crimp characteristics of

The crimp characteristics of such AN-based fibers are not limited in any way as long as they have latent or actual crimp, but the number of crimp (Cn) per 25 mm of fiber length is In terms of practical performance such as stiffness and bulk of the water-swellable fiber product that is finally obtained, it is important to have 3 or more, preferably 5 or more, and a degree of crimp (Ci) of 5% or more, preferably 7% or more. desirable.

Such AN-based fibers can be subjected to the subsequent alkali treatment process in any form such as short fibers, long fibers, fiber tows, threads, knitted fabrics, and non-woven fabrics. It goes without saying that even waste fibers that are discharged or intermediate products of the fiber manufacturing process (for example, fibers after hot drawing) can be used as the starting material in the present invention as long as they have latent or actual crimp.

In order to obtain water-swellable fibers having latent or actual crimp using such AN-based fibers as a starting material and having high water-swellability and high physical properties, only the outer layer of the AN-based fibers is selectively hydrogelized. It is necessary to form a fiber having a multilayer structure of the outer layer of the hydrogel and the inner layer of AN polymer and/or other polymer.

The water swelling degree of the fiber having a two-layer structure or a multi-layer structure produced by
-200 CC/1, and in order to have such water swelling degree and maintain sufficient fiber physical properties, COOX (COOX) is introduced into the water-swellable fiber. X: The amount of alkali metal or salt type carboxyl group represented by NH4) is 0.5 to 5. Ommol/g,
More preferably 0.5 to 3.5 mmol/? It is necessary to adjust it within the range of .

If the amount of the salt-type carboxyl group is outside the lower limit of the recommended range of the present invention, the hydrophilic or water-absorbing performance will be insufficient, and if it exceeds the upper limit of the range, the physical properties of the fiber will deteriorate and the fiber will become brittle with poor flexibility. You'll only be able to get things, which is not good.

The salt-type carboxyl group may be any one of Li, an alkali metal such as Na, or NH4, or a mixed salt of two or more thereof.

Regarding the crimp characteristics of such water-swellable fibers, there are no restrictions as long as the fibers have latent or actual crimp, and the crimp characteristics can be set as appropriate depending on the use of the fibers. However, from the viewpoint of improving various performances such as elasticity and bulkiness of the final product, in a state where crimps are made apparent, the number of crimps (Cn) is generally 3 or more and the degree of crimps (Ci) is 5
It is desirable to produce water-swellable fibers with crimp characteristics of % or more.

In addition, when processing such as spinning in the same way as normal clothing fibers, etc., the actual crimp characteristic of the water-swellable fibers is determined by the crimp number (C
It is desirable that the number of n) is 5 to 15 and the degree of crimp (Ci) is 5 to 25%.

Next, a method for hydrolyzing AN-based fibers will be described in detail.

As long as water-swellable fibers consisting of an outer hydrogel layer and an inner layer of ML polymer, etc., and having latent or actual crimp can be obtained, there are no restrictions on the hydrolysis method, but AN-based In the present invention, the following method was adopted as a one-step hydrolysis and crosslinking treatment method capable of selectively hydrogelating only the outer layer portion of the fiber.

That is, the AN-based fiber is treated with a highly concentrated alkali metal hydroxide aqueous solution of 6.0 mol/10001 solution or more (hereinafter abbreviated as method A), or 0.5 mol/10001 solution or more is applied.
1000? A low concentration alkali metal hydroxide aqueous solution coexisting with electrolyte salts at a concentration higher than that of the solution is applied (
Either method (hereinafter abbreviated as method B) was adopted.

In addition, when adopting the above method A, 6, Omol/100
When an alkaline aqueous solution with a concentration of less than 0 g solution is applied, the AN-based fibers become hydrophilic through the hydrolysis reaction but become water-soluble, making it impossible to form the outer hydrogel layer as the object of the present invention.

Also, 6.25 to 8.85 mol/10007 solution, and further 6.25 to 8.50 mol/1000? The present invention can be more effectively accomplished by using an alkaline aqueous solution in the concentration range of the solution.

Under conditions exceeding the upper limit of this preferred range, the activity of the alkali metal hydroxide decreases, requiring high-temperature treatment to increase the reaction rate, and making it difficult to remove residual alkali, which is not practical. do not have.

Furthermore, when employing method B, the amount of salt allowed to coexist is 0.
5mol/1000? When the concentration is low, below that of the solution, the AN-based fibers are made hydrophilic by the hydrolysis reaction, but most of them become water-soluble, and the outer layer of the hydrogel can be formed in one step in a low-concentration alkaline aqueous solution. It is not possible.

Also, a salt concentration of 1.0 mol/1000 g solution or more, or the salt concentration and 0.25 to 6.0 mol/10001 solution, more preferably 0.5 to 5.0 mol/10001
By using an alkaline aqueous solution having the alkali metal hydroxide concentration of the solution, the present invention can be carried out more industrially.

Regarding method A, the patent application filed by the applicant in 1972- It is described in further detail in the specification of No. 158423.

Here, examples of the alkali metal hydroxide used in the present invention include hydroxides of alkali metals such as Na, Li, etc., and mixtures thereof; Any salt can be used as long as it is stable under the treatment conditions, and the cationic components constituting the salt are, for example, Ma, alkaline metals such as Li, alkaline earths such as Be, Mg, Ca, Ba, etc. Other metals such as Cu, Zn, AI, Mn, Fe, Co, Ni, etc., and anionic components such as hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, chromic acid, dichromic acid, etc. Examples include one type or a mixture of two or more types of salts composed of acid groups such as chloric acid, hypochlorous acid, organic carboxylic acids, and organic sulfonic acids.

In addition, when using electrolyte salts in which the above-mentioned cationic component is an element with a valence of 2 or more, the outer layer of the resulting hydrogel tends to aggregate and coalesce, and the degree of swelling decreases. It is preferable to use salt as an ingredient.

Furthermore, as a solvent in place of water, methanol, ethanol, and propatool can be used as long as they do not dissolve the AN fibers to be treated.

An aqueous mixed solvent of water and a water-miscible organic solvent such as 2-methoxyethanol, 2-ethoxyethanol, dimethylformamide, dimethylsulfoxide, etc. can be used, and if necessary, other inorganic substances or organic substances can be used. It is also possible to allow substances to coexist.

Here, although the alkaline hydrolysis treatment under the conditions of the known technology actually produces only a water-soluble polymer, the specific conditions of the above-mentioned method A or B recommended for the present invention are adopted. This produces hydrogels in a single step and in high yields, which are significantly different from the results expected from reactions under known conditions.

The mechanism of action is, in particular, side reactions that form intermolecular crosslinks or intramolecular cyclic structures accompanying the hydrolysis reaction of dilyl groups in the outer fiber layer.
This can be explained by the fact that it progresses specifically under the above-mentioned specific conditions, but the details have not yet been elucidated.

In addition, as for the reaction conditions such as temperature conditions and treatment time when making the alkaline aqueous solution act as mentioned above, the preferable range of conditions varies depending on the fine structure of the polymer such as the form of the polymer, crystallinity, etc., depending on the alkali concentration, etc. Although it is impossible to define it unambiguously, in general, the higher the reaction temperature, the higher the reaction rate and the more advantageous the treatment effect can be achieved, so it is preferably 50°C or higher, more preferably 80°C or higher. The present invention can be effectively practiced by using temperature conditions of .

Further, although there are no strict limitations on the amount of alkaline aqueous solution treated with the AN fiber, at least 3 parts by weight, preferably 4 parts by weight or more of the aqueous solution should be used per 1 part by weight of the fiber. Desirably, under such conditions, the fibers can easily come into contact with the aqueous solution, and the hydrophilization reaction and crosslinking reaction of the present invention can proceed effectively.

Furthermore, as a method for applying an alkaline aqueous solution to AN-based fibers, short fibers cut into arbitrary fiber lengths are suspended in an aqueous solution, and then cut using a shearing device such as a screw type stirring device, a mixer, or a shearing device such as a Ni-Goo. A method of stirring or kneading using a kneading device etc., a method of running continuous fibers such as long fibers, fiber tows, threads, knitted fabrics, non-woven fabrics, etc. in the aqueous solution under tension or under no tension, or A wide range of known heterogeneous treatment methods can be selected, such as a method in which the short fibers, long fibers, etc. are filled in a mesh container and shaken in an aqueous solution, and a method in which heat treatment is performed after impregnation with a treatment liquid.

When producing a fiber having a multilayer structure of an outer hydrogel layer and an inner layer of AN polymer and/or other polymers by applying an alkaline aqueous solution to AN fibers, It is important to control the amount of salt-type carboxyl groups (-coox), which has a particularly close relationship with the degree of water swelling and physical properties of the fibers.

As a means for controlling the amount of salt-type carboxyl groups,
Type, part composition, crystallinity, single fiber fineness, etc. of the AN fiber to be treated, or hydrolysis treatment conditions, i.e. concentration of alkali metal hydroxide and/or electrolyte salts, temperature during hydrolysis, fiber to be treated It is possible to vary the amount of alkaline aqueous solution treated, the treatment time, etc., and it is difficult to define it unambiguously, but the hydrolysis treatment conditions, especially the treatment time, are approximately 40 minutes or less, preferably By adjusting the time within the range of 2 to 30 minutes, the object of the present invention can be easily achieved.

When hydrolyzing a fiber made of a single AN-based polymer for a long period of time exceeding the recommended range of the present invention, the inner layer of the AN-based polymer may completely disappear or the inner layer may Even if it remains, it is not desirable because the amount is small or the boundary between the outer layer and the inner layer becomes unclear, making it impossible to obtain water-swellable fibers with satisfactory physical properties.

After removing the alkali metal hydroxide remaining in the water-swellable fiber thus obtained by washing with water or the like,
If necessary, a treatment such as converting the salt-type carboxyl group into an alkali metal or ammonium salt is performed by a known method, and then, if desired, a drying treatment is performed to form a dry product.

As a result, it is possible to obtain water-swellable fibers that are composed of an outer hydrogel layer and an inner layer of an AN polymer and/or other polymer, and that have latent or actual crimp. is 3-300cc/g, preferably 5-200C
In addition to having a water swelling degree of C/g, the performance of fiber properties such as wet and dry strength, wet and dry elongation, and knot strength is almost comparable to that of ordinary AN-based clothing fibers (for example, dry strength of 2.5g).
0 g/d or more, wet strength 1.57/d or more).

In addition, since the fiber has an inner layer made of an AN polymer or the like, it also has a unique property of not undergoing dimensional change in the length direction even in a swollen state.

The water-swellable fiber of the present invention, which has such a two-layer or multilayer structure and has latent or actual crimp, has excellent water-swelling performance and an inner layer made of an AN polymer and/or other polymer. Because it has crimps, it exhibits excellent physical properties such as strength and elongation, flexibility, and stiffness. Also, because it has crimps, it has excellent properties such as stiffness and bulk in the final product. It is a noteworthy advantage of the present invention that it exhibits the following characteristics.

In addition, it does not require the use of fibers made of polymers with special compositions containing cross-linking monomers as copolymerization components, and it is possible to use ordinary AN fibers or wastes discharged from the AN fiber manufacturing process. By using fibers as a starting material and performing a one-step treatment process with an alkaline aqueous solution, fibers with high water swelling performance and excellent physical properties can be obtained.Fibers with high water swelling performance and excellent physical properties can be obtained by adjusting the alkali treatment conditions. Another characteristic advantage of the present invention is that physical properties can be controlled appropriately.

The water-swellable fiber of the present invention, which has such high water-swellability and excellent physical properties, can be used alone or by blending or making with existing natural, semi-synthetic or synthetic fibers, etc.
As a new fiber material with outstanding hygroscopicity, water absorbency, and water retention, it can be used for diapers, sanitary products, filter paper, etc., or as a dehydration material from organic solvents that are immiscible with water, sealing materials, cation exchange fibers, etc. Furthermore, like existing hydrogel powders, it can be applied to instant sandbags, artificial soil, drainage, heat/cold insulation materials, etc.

In order to further facilitate understanding of the present invention, examples are described below, but the gist of the present invention is not limited in any way by the description of these examples.

It should be noted that all percentages and parts described in the Examples are based on weight unless otherwise specified.

In addition, the degree of water swelling, the amount of salt-type carboxyl group (-COOX), the bulkiness, and the elasticity described in the following examples were measured or calculated by the following methods.

(1) Degree of water swelling (cc/g) A sample fiber of 0.11 was immersed in pure water and kept at 25°C for 24 hours.
After a period of time, the fibers were wrapped in a nylon filter cloth (200 mesh) and the water between the fibers was removed using a centrifugal dehydrator (3G x 30 minutes, where G is gravitational acceleration).

The weight of the sample prepared in this way is measured (wty
).

Next, the sample is dried in a vacuum dryer at 80° C. until it reaches a constant weight, and the weight is measured (W2P).

From the above measurement results, it was calculated using the following formula.

Therefore, the water swelling degree is a numerical value indicating how many times the weight of the fiber can absorb and retain water.

(2) -COOX base amount (mmol/?) Accurately weigh approximately 11 of the sufficiently dried sample (xy), add 20
After adding 0ml of water, while heating to 50°C, IN hydrochloric acid aqueous solution was added to adjust the pH to 2, and then to 0.0ml. A titration curve was determined using an IN aqueous sodium hydroxide solution according to a conventional method.

The amount of caustic soda aqueous solution consumed by carboxyl groups (Ycc) was determined from the titration curve.

From the above measurement results, it was calculated using the following formula.

In addition, when polyvalent cations are included, it is necessary to determine the amount of these cations by a conventional method and correct the above formula.

(3) Bulky property (om2/l) and lumbar property (P/l) After opening the sample fiber by approximately 1.01, measure the weight of the test piece created by stacking it in a 10 x 10 (Cm) rectangle. (W
3? ).

Next, the test piece was tested at a speed of 5?Lomm/min using a constant speed compression tester. Compression and unloading were repeated three times to a compression load of /cm2, and the thickness (hocm) of the test piece at the initial load of 0.51/cm2 was determined from the third compression curve, and the bulkiness was calculated using the following formula.

The above compression-unloading process was repeated three times, and then the test piece was
0? The compression work (waist strength) was calculated as the integral value of the thickness of the test piece and the compression load from the compression curve obtained by compressing to a load of /cm.

Example: Composite bonding type AN-based composite fiber (Japan Exlan Kogyo ■
made, single fiber fineness: 6d, fiber length: 51mm) 5 parts to 30
% (7.5 mol/1000P solution) The fibers are immersed in 95 parts of aqueous caustic soda solution, boiled for 10 minutes while stirring, and then washed with water to remove residual alkali in the fibers, dried to give a water-swollen white to slightly yellow color. The fibers (I) were formed.

The obtained fiber (I) did not dissolve in water, and when the fiber (I) was squeezed in a water-swollen state, it was confirmed that the AN polymer core remained.

In addition, the amount of the fiber (I) is 2.6 mmol/? -COON
It contained an a group.

In addition, the results of measuring various physical properties of the fiber (I) are listed in Table 1 together with the physical property values of the AN fiber to be treated.

As is clear from the results in Table 1, although the water-swellable fiber (I) according to the present invention has excellent water-swelling performance, both the crimp property and the strength and elongation are at reference values. It can be seen that the level is maintained at a level almost comparable to that of treated ml-based composite fibers).

On the other hand, as a comparative example, 10% (2.5 mol/1000
The process was carried out according to the above recipe except that a 23% (5,75 mo171000 g solution) caustic soda aqueous solution was used. In both cases, the treated AN
The system composite fibers only dissolve in an aqueous solution to form a viscous solution, and when such a low concentration aqueous solution of caustic soda alone is used, it is not possible to form them into the water-swellable fibers that are the object of the present invention. Ta.

In addition, 35% (6%) of caustic potash can be used instead of the above-mentioned caustic soda.
,25mol/1000? Solution) When the treatment was carried out according to the above recipe except that an aqueous solution was used, fibers which were white to slightly yellow in color, substantially water-insoluble and water-swellable, and had crimps were obtained.

Example 2 Two-component bonded AN-based composite fiber described in Example 1 (however,
Fiber length: 10 mm), single component AN with mechanical crimping
System fiber (AN=90%, single fiber fineness: 6d, fiber length: 1
0mm, Cn=9°01Ci=10.0) and 5 parts each of the single component AN fiber without crimping, 20
% (1.5 mol/1000 g solution) of sodium chloride coexisted with 95 parts of a 10% (2.5 mol/1000 f solution) caustic soda aqueous solution, and three types of water-swellable fibers ( ■～■) were produced.

It was confirmed that none of the three types of fibers (■ to ■) thus obtained were dissolved in water, and that the AN polymer core remained.

The results of measuring various physical properties of the fibers (■ to ■) are listed in Table 2.

As is clear from the results in Table 2, the water-swellable fibers with crimps (■ and ■) according to the present invention have higher bulkiness and lower waist than the water-swellable fibers without crimps (■). The fact that sex is significantly improved is understood.

Moreover, such a tendency for improvement in performance is remarkable in the fiber (n) which employs a self-crimping type fiber (ie, the above-mentioned composite fiber) as a starting material among the products of the present invention.

In addition, when only the hydrolysis treatment time of the above-mentioned two-component bonded AN-based composite fiber was extended to 1 hour, the obtained fiber (V) was 3.4 mmol/? Although it contains COONa groups of confirmed.

Example 3 In the formulation described in Example 2, sodium nitrate was used instead of 20% Glauber's salt, and the concentrations of the salt and caustic soda were varied as shown in Table 3 to produce the AN-based composite fiber described in Example 2. processed.

All of the 10 types of water-swellable fibers (■ to XV) obtained had crimps.

The results of measuring the degree of water swelling and the amount of -COONa groups of the fibers (■ to XV) are also listed in Table 3.

From the results in Table 3, it is clear that when the concentration of salt coexisting in the alkaline aqueous solution is below the range recommended for the present invention (sample No.
, XV), only fibers with a low degree of water swelling were obtained, and the yield of the desired water-swellable fibers was as low as about 40% because the amount of water-soluble polymer produced was significantly increased.

Further, in sample AM [that is, when the alkali concentration was extremely low], fibers having the desired degree of water swelling could not be obtained.

Furthermore, it is clear from Samples No., ■, ■, ■, and ■ that even if the alkali concentration is constant, fibers with various degrees of water swelling can be produced by changing the salt concentration.

Example 4 Two-component bonded AN-based composite fiber (single fiber fineness: 2.5
d, Cn=15 pieces/25mm after boiling for 10 minutes, C1=
37%) was treated in a 30% caustic soda aqueous solution under tension such that C1 = 13% (treatment temperature: 95°C, treatment time: 25 minutes), it exhibited a white to slightly yellow color,
0.6 mmol/? A water-swellable fiber (X■) containing -COONa groups and having a water swelling degree of 37 cc/g was obtained.

The thus obtained crimped fiber (XVI, Cn-1
1 piece/25 mm, C1=13%) was carded, and there were no problems with the fiber opening or entanglement.

Claims (1)

[Scope of Claims] 1 It is composed of an outer layer made of a hydrophilic crosslinked polymer and an inner layer made of an acrylonitrile polymer and/or other polymer, and has latent or actual crimp, and -COO
The salt type carboxyl group represented by X (X: alkali metal or NH4) is 0.5 to 5.0 mmol/? A novel water-swellable fiber having a degree of water swelling of 3 to 300 CC/g and high physical properties. 2. A highly concentrated aqueous alkali metal hydroxide solution of 6.0 mol/1000 g solution or more, or 0
．． The outer layer portion of the fiber is hydrophilically crosslinked by applying a low concentration alkali metal hydroxide aqueous solution coexisting with an electrolyte salt at a concentration of 5 mol/1000 g solution or higher to form an outer layer portion made of a hydrophilic crosslinked polymer. an inner layer made of an acrylonitrile polymer and/or another polymer, and has latent or actual crimp, and -COOX (
X: Contains 0.5 to 5.0 mmol/g of salt type carboxyl group represented by alkali metal or NH4), and 3 to
300CC/? 1. A method for producing a novel water-swellable fiber, which comprises forming the fiber into a fiber having a degree of water swelling and high physical properties. 3.0 as a low concentration alkali metal hydroxide aqueous solution.
5mol/1000? 3. The manufacturing method according to claim 2, wherein an aqueous alkali metal hydroxide solution having a concentration of 0.25 to 6.0 mol/1000 g of solution is used, in which electrolyte salts are present at a concentration higher than that of the solution.